This invention is directed to weld inspection and, more particularly, to ultrasonic weld inspection.
In certain environments, it is necessary that welds bonding two pieces of metal (e.g., panels) together be completely flawless so that no small discontinuities that will serve as "crack starters" exist. (Such discontinuities may grow into cracks under cyclic loading by "in service" forces, ultimately resulting in structural failure.) One technological area where welds having this degree of integrity are required is in ship building. In the past, such integrity has been required of ships' hulls. More recently, large hydrofoils developed for oceangoing hydrofoil ships require welds having a similar level of integrity. Obviously, the visual inspection of a weld cannot provide the assurance that the required weld integrity exists. That is, while visual inspection will detect large visable weld flaws, in general, minute weld flaws will not be detected. Further, visual inspection will miss even large flaws if they are totally located inside of the weld. For these reasons other techniques for inspecting welds to determine whether or not they possess an adequate level of integrity have been developed.
One such technique uses ultrasonic principles. In some ultrasonic systems an ultrasonic beam, produced by an ultrasonic transducer located on a surface of the welded part to be inspected, is directed toward the weld and specular beam reflections, caused by weld flaws, are detected. In the past, the ultrasonic transducers used in such systems have been manipulated by hand through a path of travel that is intended to ensure that the ultrasonic beam scans the entire weld volume to be inspected. The path is complex and may require moving the transducer both parallel to the weld at a relatively slow rate and transversely with respect to the center line of the weld. Simultaneously, the transducer is angularly oscillated back and forth. Usually, oil is spread on the surface of the welded part or panel to provide an ultrasonic beam coupling medium, and flaws are detected by watching for the appearances of peaks on a cathode ray tube (CRT) display, which denote the receipt of specular reflections created by the ultrasonic beam intersecting a weld flaw. Reflections having an amplitude exceeding a predetermined level are interpreted as rejectable flaw indications, unless they can be related to some known reflecting surface within the structure. If a rejectable flaw indication is found, the inspector manipulating the ultrasonic transducer attempts to identify the flaw, and usually marks its location directly on the weld.
While hand-scan methods have been successfully used to locate rejectable flaws in welds, this technique is unsatisfactory for a variety of reasons. For example, there is no way of assuring that freehand guidance of the transducer will result in 100% coverage of the weld volume. As noted above, the inspector is simultaneously required to: (1) manipulate the transducer in a complex scanning pattern; (2) ensure that sound is coupled uniformly into the test part; and (3) observe a complex oscilloscope trace to sort and analyze echo signals. Obviously, it is physically and mentally exhausting to perform these tasks over an extended period of time. Further, it is impossible, using hand-scanning ultrasonic techniques, to obtain meaningful recordings of actual ultrasonic flaw indications (i.e., reflected signals) because it is impossible to sense the exact position of the hand and, thus, the exact position of the transducer, when a flaw echo signal is received. Obviously, recordings are helpful in identifying the kind of flaw that is producing a given signal and in separating marginal signals from background noise. Further, records free an inspector from having to continuously watch an oscilloscope trace, and ease the task of communicating the results of an inspection to other persons. Moreover, without recordings, it is difficult to prove that a given weld has actually been inspected. In addition, reproducibility is difficult to obtain using hand-scanning techniques. That is, it has been found that two different inspectors working on the same section of weld often obtain different results. Finally, freehand ultrasonic weld inspection is time-consuming, and therefore costly. In this regard, it has been found that an inspection rate of one-half hour per foot of weld is not uncommon.
In view of the foregoing difficulties, various proposals have been made to automate ultrasonic weld inspection. For a variety of reasons, the resultant systems have not been entirely satisfactory. In most instances, prior art mechanical ultrasonic weld inspection apparatus, capable of moving a transducer through a relatively complex path of travel, have not been portable. Other also relatively large and nonportable devices have used "immersion techniques", involving a large tank of water into which parts are immersed. Obviously, those devices have the disadvantage of requiring the time-consuming, and therefore costly, transportation of parts from an assembly area to an inspection area, and the subsequent return of the parts to the assembly area for removal of weld flaws or further assembly to other structures.
While some portable ultrasonic weld inspection devices have been proposed, these devices also have disadvantages. The primary disadvantage is their general inability to provide complex transducer motion. Specifically, such devices have generally provided orthogonal transducer motion, but not oscillatory transducer motion. Another disadvantage of many such devices is that, while portable, they are still large, heavy, and inflexible.
A further disadvantage of many types of prior art ultrasonic weld inspection systems, regardless of whether or not they are portable, is their inability to produce adequate displays and/or usable hard copy and video recordings.
Therefore, it is an object of this invention to provide a new and improved ultrasonic weld inspection apparatus.
It is a further object of this invention to provide a portable, mechanized scanning ultrasonic weld inspection system.
It is a another object of this invention to provide a portable mechanized scanning system suitable for moving a transducer through a complex path of travel.
It is a still further object of this invention to provide a new and improved display and/or recording subsystem for an ultrasonic weld inspection system.
It is yet another object of this invention to provide a mechanical scanning, display and recording ultrasonic weld inspection system.